1. Field of the Invention
The present Invention relates to an equipment which composes and outputs color images in color copying machines, color printers, and the like, and particularly to the edge processing system which is built into such a color image processing system and performs the edge emphasizing and edge attenuating processes by detecting the edge on the original sheet as read by the system.
2. Description of the Prior Art
Digital color image forming equipments, such as color copying machines and color laser printers, are loaded with the toners in the four colors, which are Y (yellow), M (magenta), C (cyan), and K (black), in the case of full-color reproduction and reproduce the color images by applying and developing the color toners in layers. In other words, a full-color copy is completed only by executing the copying process four times. Therefore, for the reading and reproduction of an original sheet in color as placed over the platen, the machine first reads the original sheet optically and converts the signal thereby obtained into the signals for the individual toners, and then, for the rendition of halftone images, such as photographs and pictures, it is necessary for such equipment to perform highly advanced image processing operations for achieving the reproduction of the colors and chromatic gradation of such images.
FIG. 55 is a chart illustrating the construction of a digital color image processing system, FIG. 56 is a chart illustrating an example of the construction of the conventional edge emphasizing process circuit, FIG. 57 is a chart illustrating the construction of a hue detecting circuit, and FIG. 58 is a chart for illustrating the edge emphasizing process.
In color copying machines in general, it is observed that the required memory capacity will be too large if the image signals obtained by one scanning operation for the reading of the original sheet are to be stored in memory for the execution of the copying process for four times, and, consequently, the conventional color copying machine performs the scanning operation for the reading of the original sheet in repetition every time each copying process is executed, thus performing the processing of the signals. In this reading process, the system detects the signals optically as separated into those for the three colors, B (blue), G (green), and R (red), and thereafter converts the signals into the color toner signals for Y, M, and C through the END conversion device 401 and the color masking device 402 as illustrated in FIG. 55. Then, the machine performs the generation of the black plate and the elimination of the undercolor by means of the UCR 403, and converts the toner signals X for the developed color into the ON/OFF binary value data passing the said toner signals through the hue separation type nonlinear filter, the TRC 410 (the tone regulating controller), and the SG (the screen generator) 411. And, the machine controls the laser beam with these binary value data, thereby reproducing halftone images by development in mesh dot in chromatic gradation.
Usually, a digital color image processing system processes images containing the binary value images, such as characters and line drawings, in mixture with the halftone images, such as photographs and printed matters in mesh dots. Therefore, the present Applicant has separately proposed a system which performs the edge emphasizing process with a nonlinear filter introduced for the purpose of copying those original sheets which have such different kinds of images thereon.
Into the hue separating type nonlinear filter section are input eight-bit signals as classified for each single color according to the developing process by disintegrating the signals generated on Y, M, C, K after the undercolor eliminating process. Here, the input signals are divided into two systems, one performing the smoothing process and the other performing the edge emphasizing process, and these signals are ultimately synthesized and put out as the nonlinear filter signals. It is FIG. 56 that shows an example of the construction of the edge emphasizing process circuit. In the edge emphasizing process, the hue of the input images is detected by the hue detecting circuit 405, and it is determined whether the developed color at that moment is a necessary color or an unnecessary color. If the input image represents a black region, the system does not perform any edge emphasis for the colored signals for Y, M, and C, but controls the K signal alone for emphasis thereof in proportion to the amount of the edge.
The hue detecting circuit 405 is provided, as shown in FIG. 57 (a), with the maximum-minimum circuit 412, which obtains the maximum value and the minimum value of the Y, M, and C, a multiplexer 413, which selects the developed color, the deducting circuit 414, which calculates the difference between the maximum value and the minimum value, and comparators 416 through 418. These comparators 416 through 418 compares the difference values thus obtained with the threshold value and sets the output for r, m, c', m', and y' respectively at the logical value "1" in case the said comparators find that the said difference values are larger than the said threshold value. Then, from this output, the system derives a determining hue under the determining conditions shown in FIG. 57 (b), and further the system determines whether the particular developed color is a necessary color (to be expressed as "1") or an unnecessary color (to be expressed as "0") as judged on the basis of the determining conditions for the necessary color and the unnecessary color as presented in FIG. 57 (c). Thus, the determining hues are set up for application to the eight colors, W (white), Y, C, B, G, R, and K, which are used for the colors of the ordinary characters.
As it is clearly seen in the determining conditions for the necessary colors and the unnecessary colors, the system determines the developed colors m and c as the necessary colors in case the hue is B, for example, while it determines the other colors to be unnecessary colors. Accordingly, the system generates in this case the signals for emphasizing the edge in the cycles for the necessary colors with the operation of (1) of the LUT 408 for edge emphasis while it generates the signals for not emphasizing the edge in the cycles for the unnecessary colors with the operation of (2) of the LUT 408 for edge emphasis.
In the operation with the system mentioned above, however, smoothing signals remain in the signals for the colors, Y (yellow), M (magenta), and C (cyan) although it achieves improvements on the reproduction of the characters in black as compared with the conventional system, which emphasizes all of the Y, M, C, and K signals. In specific terms, the system merely emphasizes the necessary colors with (1) while it eliminates the unnecessary colors with (2) as shown in the LUT 408 for edge emphasis illustrated in FIG. 56, and the system, therefore, generates the edge emphasizing process signals which emphasizes only K without emphasizing Y, M, and C in the processing of filter input signals for black characters as shown in FIG. 58 (a), but, with the smoothing filter, the smoothing process signals are generated to produce a smoothing effect with respect to all of the Y, M, C, and K signals, as shown in FIG. 58 (b). Consequently, when all these signals are finally synthesized, the smoothing signals for Y, M, C, and K remain as shown in FIG. 58 (c). Ordinarily, even in the case of characters in black only, the signals for Y, M, and C, as well as the signal for K, will be loaded, so that the smoothed colors of these Y, M, and C appear in the edge area, which means that characters in black cannot be reproduced in the single color of K. With a system construction like this, there is a problem in that there occur an increase in the thickness of lines and the changes and turbidity of color in the edge due to deviations in registration or the like, with the result that the quality of the reproduced picture is thereby deteriorated.